In conjunction with a projection display, it is desirable to employ a color management system, and it is further desirable that such color management system facilitate the production of a high contrast image while accommodating a relatively high level of illuminating flux and providing for efficient packaging. Unfortunately, currently existing color management systems are capable of achieving increased contrast at practical levels of illuminating flux only by employing highly specialized materials, resulting in unreasonable increases in cost.
A color management system typically functions by first separating input light (e.g., white light) into a plurality of color channels traversing the visible spectrum (e.g. red, green and blue), then using the separate color channels to illuminate a plurality of corresponding microdisplays (e.g., LCoS microdisplays) and recombining the color channels to produce an output light (e.g., white light). Where it is desired to project an image in conjunction with the output light beam, spatial information may be superimposed into each of the color channels by the microdisplays prior to recombination. As a result, a full color image may be projected in conjunction with the output light beam. As used herein, the terms “microdisplay,” “panel,” “display,” “display panel,” and “light valve” refer to a mechanism configured for receiving an incipient light beam, imparting spatial information in the light beam, and emitting a modified light beam comprising the incipient light beam and the spatial information. An example of such a microdisplay is model number DILA SX-070 manufactured by the JVC company of Japan.
It should be noted that a microdisplay may be configured as a substantially reflective display panel or as a substantially transmissive display panel. A substantially reflective display panel is configured to emit a modified light beam toward a direction that is substantially toward the direction from which the incipient light beam came (i.e., to retroreflect). A substantially transmissive display panel is configured to emit a modified light beam toward a direction that is substantially similar to the direction in which the incipient light beam travels (i.e., to transmit a modified light beam through the panel). For example, a reflective panel may be configured to receive an incipient light beam traveling in a first direction, to impart spatial information upon the light beam, and to emit a modified light beam toward the direction from where the incipient light beam originated (i.e., reflected 180 degrees from the direction of the incipient light beam). Alternatively a transmissive panel may be configured to receive an incipient light beam, to impart spatial information in the light beam, and to emit a modified light beam in substantially the same direction as that in which the incipient light beam travels.
Prior art color management systems have thus far not sufficiently proven to be able to produce high contrast images at low cost without compromising their ability to maintain reasonable quantities of illuminating flux or to be packaged efficiently. This is due, in part, to image noise caused by optical characteristics that are inherent in all real optical elements. This is also due to the inability of currently existing color management systems to effectively separate and remove such noise from the light beam before it is projected to a display.
For example, many prior art color management systems use solid “cube-type” polarizing beamsplitters for color separation and recombination. These polarizing beamsplitters are otherwise referred to as MacNeille prisms or cube polarizing beamsplitters. “Cube type” polarizing beamsplitters are inherently susceptible to thermal gradients that typically arise at high flux levels, often causing stress birefringence which results in depolarization of the light and a loss of contrast. As a result, where high contrast images are desired, it has been necessary to use costly high-index, low-birefringence glass. Although this solution has proven effective to reduce birefringence at low levels of flux, it is expensive and exhibits reduced effectiveness at eliminating thermally induced birefringence at high flux levels (e.g., greater than approximately 500 lumens).
For example, FIG. 1 illustrates a prior art color management system 110, commonly known as the ColorQuad™ from Colorlink, in which four cube polarizing beamsplitters and five color selective retardation elements are used to provide color separation and recombination. In accordance with this system, the input cubic polarizing beamsplitter receives an input light beam 120 and separates it into three components, a green component 121, a blue component 122, and a red component 123. The red component 123 receives spatial information from a reflective red panel 133; the blue component 122 receives spatial information from a reflective blue panel 132; and the green component 121 receives spatial information from a reflective green panel 131. Finally, the output cubic polarizing beamsplitter recombines the red component 123 and blue component 122 with green component 121 to form a full color image 140, which may be received by a projection lens or other optical elements depending on the purpose of the system.
It should be noted that at high levels of light flux, cubic polarizing beamsplitter 110 typically becomes thermally loaded and necessarily distorts physically, causing stress birefringence, which often results in depolarization of the light and a decrease in contrast. Further, in addition to receiving spatial information from the red, green and blue panels in the cubic polarizing beamsplitter 110, the red, green, and blue light components also typically receive undesirable spatial information as a result of birefringence in the materials of the optical components in the red, green, and blue light paths. This undesirable spatial information tends to further decrease the contrast of the image.
In an attempt to reduce the adverse effects of the use of cube polarizing beamsplitters, various attempts have been made to implement plate polarizing beamsplitters in place of cube configurations in color management systems. However, these attempts have often given rise to other optical aberrations associated with the plate polarizing beamsplitters, such as astigmatism. Thus, it is well understood that most if not all optical elements used in today's color management systems contribute noise to, and/or otherwise corrupt, any light beam passing through, or affected by, the optical element. It should be noted that, as used herein, the terms “noise” and/or “corrupt[ion of a] light beam” refer to optical effects associated with, and/or comprising, for example, scatter, polarization rotation (e.g., non-homogenously polarized light emitted from a polarizing beamsplitter that may comprise components having undesirably rotated polarization orientations), material birefringence, and or other undesirable characteristics associated with geometries and or coatings of optical elements, and the like.
Accordingly, many color management systems also include optical filters, such as analyzers or polarizers that are configured to attempt to eliminate most or all of such noise from the light beam so that a substantial portion of the contrast of the image might be restored. These filters may attempt to eliminate such noise, for example, by separating light according to its polarization. This is made possible by the fact that the desirable light components of the light beam may be oriented with a first polarization while the noise may be oriented differently or otherwise not substantially polarized.
Unfortunately, however, as a light beam passes through, or is affected by, an optical element, the polarization of the light tends to be disturbed. Thus, a portion of the noise often becomes indistinguishable, on the basis of polarization at least, from the light that comprises the desirable image. Accordingly, the opportunity to fully and effectively eliminate noise from the light beam on the basis of polarization diminishes as the tainted light beam passes through, or is affected by, each successive optical element. Nevertheless, in prior art systems, the additional light constituents are not removed until after the corrupted light beam has passed through, or has been affected by, additional optical elements, such as a light recombiner, a prism, and/or the like.
In addition to these and other difficulties, prior art systems are often susceptible to the effects of stray light which may undesirably reach the optical components and inadvertently be combined with, or otherwise corrupt, the desirable image imparted by the panels onto the modified light beam. For example in many prior art systems, wherein the output light beam is transmitted to a projection lens or another optical component, a portion of such light may unfortunately be reflected by the component and transmitted back (i.e., retroreflected) toward and received by other system components. The reflected light, then, may be undesirably recombined with the desirable light to produce a composite light beam containing both the desirable image and, for example, a ghost of the desirable image. Accordingly, the combined ghost-bearing image may be undesirably transmitted to the display.
In addition, prior art color management systems employing transmissive panels frequently encounter extreme thermal conditions in the optical components that are positioned downstream of the transmissive panel. This common problem is caused by the need for waste light to be rejected from the modified light beam, and may occur where the panel fails to perform the elimination of such waste light. Such situations, unfortunately, are much more common with transmissive panels than with reflective panels. More particularly, in typical color management systems, the incipient light beam which is received by a panel bears a fixed intensity or brightness. The panel, then, after receiving the incipient light beam, imparts spatial information on (i.e., modifies) the light beam by modulating the intensity of light at each of a large number of discrete locations (e.g., pixels). Typically, reflective panel systems accomplish this by reflecting (i.e., emit) only the light comprising the desirable image, by absorbing the waste light and emitting the generated heat. Transmissive panels, on the other hand, typically transmit substantially all of the incipient light they receive, but impart spatial information by spatially modifying selected properties (e.g., polarization) of the light beam. Accordingly, systems employing transmissive panels frequently must rely upon a downstream optical component to reject the waste light (and heat) based on the spatially modified properties (e.g., polarization). Accordingly, as the waste light is rejected, heat is generated. The requirement that a particular component be configured to accommodate rejection of large quantities of light often imposes difficult design constraints on those optical components.
Accordingly, it would be advantageous to have a color management system that could be used in high flux projection systems while simultaneously functioning in a wide range of thermal environments with reduced birefringence sensitivity and improved durability while producing a high-contrast image. It would further be advantageous to have a color management system that could achieve these objectives without requiring costly, high index, low birefringence glass or a particular susceptibility to optical aberrations produced by polarizing beamsplitters in plate configurations. It would further be advantageous to have a color management system that could achieve these objectives while eliminating or reducing ghosts or other undesirable images caused by stray light. It would further be advantageous to have a color management system that could achieve these objectives in transmissive panel systems while relieving the extreme temperature environment difficulties associated with such transmissive panels.